Steel for high-temperature use



Patented July 14, 1953 UNITED STATES PATENT OFFICE 7 2,645,574 new:FOR'LH'YIGEI-TEMPERATURE USE Claude L. ClarlgCanton, Ohio, assignor toThe Timken Roller Bearing Company,

Canton,

Ohio, a corporation of Ohio No Drawing. Application September 11, 1951,

' Serial No. 246,159

This invention relates to steels that combinedesirable properties atnormal temperatures with excellent high temperature properties.

Certain parts of jet engine and gas turbines, such as their rotors, andparts of aircraft superchargers and related devices operate at highstress and elevated temperatures. Various steels have been developed forsuch purposes, for instance the well-known steel alloy disclosed inUnited States Patent No. 2,398,702. In general, the steels used for suchpurposes up tothepresent time have been highly alloyed, and it ischaracteristic of them that they are either very dimcult to fabricate orthey require special heat treatments of long duration and, in someinstances, are rather complicated.

The present shortage of certain critical metals has created the need forsteels of low alloy content that are also adapted to replace the highlyalloyed steels used up to the present time for the foregoing purposes.In particular, there is a demand for steels containing a maximum of 5per cent of alloying elements and which possess a 1000-hour rupturestrength at 1100 F. in excess of 30,000 pounds per square inch (p. s.i.). Steels meeting those requirements have not been availableheretofore.

It is among the objects of the invention to provide low alloy steelshaving a satisfactory combination of high temperature properties, andparticularly a rupture strength at 1000 hours and 1100 F. exceeding30,000 pounds per square inch.

A further object is to provide steels in accordance with the foregoingobject that likewise possess desirable physical properties at normaltemperatures.

Still another object is to provide steels embodying the foregoingobjects and whose properties are developed by a simple and short heattreatment.

Yet another object is to provide steels in accordance with the foregoingobjects containing not over about 5 per cent of alloy content.

The invention is predicated upon my discovery that its stated objectsare attained with steels containing from about 0.15 to 0.5 per cent ofcarbon, from about 0.75 to 2.5 per cent of chromium, from about 0.2 to1.0 per cent of manganese, from about 0.25 to 1.0 per cent ofmolybdenum, from about 0.1 to 1.5 per cent of silicon and from about 0.2to 1.0 per cent of vanadium. The remainder of the steels consists ofiron together with impurities and elements in amounts that do notadversely affect the properties that characteriz the steels of thisinvention. For full 3 Claims. (01. 'i5.126)

development of those properties the steels should not contain over about0.04 per cent each of phosphorus and sulfur.

- Within the foregoing limits I now prefer that the steels contain fromabout 0.18 to 0.28 per cent of carbon, from about 1 to 2 per cent ofchromium, from about 0.3 to 0.6 per cent of manganese, from about 0.4 to0.6 per cent of molybdenum, from, about 0.5 to 1.0 per cent of silicon,and from about 0.7 to 0.9 per cent of vanadium.

Steels of the foregoing composition are readily fabricated by all hotforming operations such, for example, as forging, rolling, and piercinginto seamless tubes. likewise, they can be welded readily.

The best combination of strength and ductility at both room temperatureand at 1100" F. is developed by air cooling, or normalizing, the steelsfrom 1750 F. or higher, followed by tempering at about 1200 F. to about300/350 Brinell. This heat treatment produces a martensitic structure.

The excellent properties of these steels and th high degree of shockresistance that they possess at elevated temperatures ischaracteristically exemplified by the properties of a steel inaccordance with the invention and containing 0.22 per cent of carbon,1.34 per cent of chromium, 0.55 per cent of manganese, 0.54 per cent ofmolybdenum, 0.6 per cent of silicon, 0.84 per cent of vanadium, 0.015per cent of phosphorus and 0.023 per cent of sulfur. This steel whenheat treated in the manner just described has the following roomtemperature properties:

Tensile strength p.s.i 139,500 Proof stres p. s. 1.. 102,250 0.2% yieldstrength p. s. i 114,000 Elongation in 2" "percent" 17.5 Reduction ofarea do 64 Brinell hardness 321 In addition to a rupture strength after1000 hours at 1100 F. of 33,000 p. s. i., this steel showed thefollowing tensile properties at 1100 F.:

Tensile strength p.s.i 71,000 Proportional limit p. s. i 32,500 0.1%yield strength p.s.i 59,500 0.2% yield strength p. s. i 64,000Elongation in 2" percent 25 Reduction of area do 69 Such propertiesadapt these steels for the making of parts that are subjected to highstress at such high temperatures as 1100 F., and 0bviously theyrepresent a major saving of critical alloying elements in comparisonwith the presently used alloy steels containing several times as much asalloy content as is present in these steels. The properties of thesesteels adapt them excellently for other purposes also, such as foraircraft brake discs.

According to the provisions of the patent statutes, I have explainedtheprinciple and mode of practicing my invention and have described WhatI now consider to represent its best embodiment.

as specifically described.

I claim:

1. A forgeable steel alloy which. as normalized from 17 50 F. andtempered at 1200 F. to-aBrinell However, I desire tohave it understoodthat, within the scope of the appended claims, the invention may bepracticed otherwise than sulfur.

hardness of 300/350 is characterized by high strength at room andelevated temperatures and by a 1000 hour rupture strength at 1100 of atleast 30,000 pounds per square inch and having substantially thecomposition: 0.18 to 0.28 per cent of carbon, 1 to 2 per cent ofchromium, 0.3 to 0.6 per cent of manganese, 0.4 to 0.6 per cent ofmolybdenum, 0.5 to I per cent of silicon, and 0.7 to 0.9 per cent ofvanadium, and the remainder iron together With impurities and elementsin amounts that do not adversely aflect the properties.

' 2. A hot worked and heat treated articleformed of steel havingsubstantially the composition: 30

0.18 to 0.28 per cent of carbon, 1 to 2 per cent of 4 chromium, 0.3 to0.6 per cent of manganese, 0.4 to 0.6 per cent of molybdenum, 0.5 to 1per cent of silicon, and 0.7 to 0.9 per cent of vanadium, and theremainder iron, the article as normalized from 1750 F. and tempered at1200 F. to a Brinell hardness number of 300/350 having high strengthatrooni and'felevated"temperatures and a 1000 hour rupturestrength at1100" For at least 30,000

pounds per square inch. 7

'3. Steel according to claim 1 containing not over about. 0.04per centeach of phosphorus and CLAUDE L. CLARK.

References Cited in thefile of this patent UNITED STATES PATENTSorrnERREFERENcEs The Iron Age, August 2:, 1945, pages 58 to 63.

1. A FORGEABLE STEEL ALLOY WHICH AS NORMALIZED FROM 1750* F. ANDTEMPERED AT 1200* F. TO A BRINELL HARDNESS FO 300/350 IS CHARACTERIZEDBY HIGH STRENGTH AT ROOM AND ELEVATED TEMPERATURES AND BY A 1000 HOURRUPTURE STRENGTH AT 1100* F. OF AT LEAST 30,000 POUNDS PER SQUARE INCHAND HAVING SUBSTANTIALLY THE COMPOSITION: 0.18 TO 0.28 PER CENT OFCARBON, 1 TO 2 PER CENT OF CHROMIUM, 0.3 TO 0.6 PER CENT OF MANGANESE,0.4 TO 0.6 PER CENT OF MOLYBDENUM, 0.5 TO 1 PER CENT OF SILICON, AND 0.7TO 0.9 PER CENT OF VANADIUM AND THE REMAINDER IRON TOGETHER WITHIMPURITIES AND ELEMENTS IN AMOUNTS THAT DO NOT ADVERSELY AFFECT THEPROPERTIES.